A vector is an organism which carries a disease from plant to plant. Sap sucking insects such as aphids often act as vectors, collecting the pathogen from the sap of one plant and injecting it, along with salivary juices, into a healthy plant.

Vectors are the most common method of viruses spreading from one plant to another. Some viruses can survive and multiply in the vector’s body for several weeks and therefore may be spread to many different plants.